1. Field of the Invention
The present invention relates to a semiconductor device, and in particular, relates to a semiconductor device having a rectifier circuit configured with a thin film semiconductor element. The invention also relates to an electronic apparatus using a semiconductor device having a rectifier circuit.
2. Description of the Related Art
In recent years, mobile phones have been widely used with the advance of communication technology. In future, transmissions of moving images and of more information are expected. In addition, through reduction in weight of personal computers, those adapted for mobile communication have been produced. Information terminals called PDAs originated in electronic notebooks have been also produced in large quantities and widely used. With the development of display devices, the majority of portable information devices are equipped with a flat panel display.
In particular, a display device having both a pixel and a driver configured with a thin film transistor by using a technology called a low-temperature polysilicon for forming polysilicon over a glass by laser annealing has been widely used recently. In addition, circuits using the low-temperature polysilicon technology have been developed, and a CPU, a memory circuit, and the like using the technology are released. The application of the low-temperature polysilicon technology to an analog circuit may be realized sooner or later.
By such an analog circuit, nonelectrical data from outside of a display device such as a sound and a pressure can be detected. A sound signal is converted into an electrical signal by a microphone and the electrical signal is amplified, and then converted into direct current by a rectifier circuit or a smoothing circuit. The nonelectrical data can be detected based on the direct current potential.
In the case where the rectifier circuit can be configured with a thin film transistor over an insulating substrate, a display device using low-temperature polysilicon can be configured more systematically.
A rectifier circuit is generally configured by a diode and an operational amplifier as shown in FIG. 3. Such rectifier circuit is well known and frequently employed due to its simple configuration in the case of structuring an electronic apparatus (see Non-Patent Document 1, for example).
[Non-Patent Document 1]
‘Standard Text for OP-Amp Circuit Design’, CQ publisher, p. 316
An operation of a circuit shown in FIG. 3 is explained hereinafter. Considered first is the case where a signal with a potential higher than that of a power source 309 is inputted to an input terminal 307. A potential of an inverting input terminal of an operational amplifier 301 is equal to that of a non-inverting input terminal and the non-inverting input terminal is connected to the power source 309, therefore, the potential of the non-inverting input terminal is equal to that of the power source 309. Accordingly, current flows from the input terminal 307 toward the inverting input terminal. The current flows into an output terminal of the operational amplifier 301 through a diode 303. An output potential of the operational amplifier 301 becomes lower than the potential of the power source 309 by one VF of the diode 303. Each potential at both ends of a resistor 305 is equal to that of the power source 309 because no current flows into the resistor 305 in this case.
Considered next is the case where a signal with a potential lower than that of the power source 309 is inputted to the input terminal 307. Current flows from the output terminal of the operational amplifier 301 into the input terminal 307 through a diode 302, the resistor 305, and a resistor 304 in this case. A signal of the opposite phase to the input signal is outputted to a connection point between the resistor 305 and the diode 302. FIG. 4A shows an input signal and FIG. 4B shows an output after the rectification. It is noted that the reference numeral 306 refers to a smoothing circuit and 308 refers to an output terminal.